A typical elevator system comprises an elevator car and a counterweight, each suspended on opposite ends of hoist ropes, belts, cables, or the like, and movably disposed within an elevator hoistway. Elevator systems further include a set of guiderails generally extending the length of the hoistway and disposed on opposing sides of the hoistway to evenly guide the elevator car therethrough. Roller guide assemblies rigidly coupled to the elevator car are configured with rollers which roll along the guiderails as the elevator car travels through the hoistway. Because of their direct interaction with the guiderails, the design of the roller guide assemblies and the associated rollers may be the most influential variable in improving the ride quality of elevators.
Various factors may affect the ride quality as experienced by passengers of an elevator car as it travels through an elevator hoistway. Among other things, elevator cars may be subjected to lateral vibrations or relatively low offset loads as the rollers of the roller guide assembly move over any unevenness or imperfections in the guiderails. Elevator cars may also be subjected to higher offset loads caused by, for example, any significant movement of passengers within the elevator car, the loading or unloading of passengers, or the like. Currently existing elevator systems employ different roller guide configurations, such as suspension mechanisms and/or elastomeric roller materials, to provide adequate stiffness and to dampen the offset loads which cause ride discomfort. While such roller guide mechanisms may provide adequate stiffness and dampening, there is still room for improvement.
Some elevator systems employ roller guide assemblies having suspension mechanisms which support the rollers on movable roller axes. In particular, the suspension flexibly biases the rollers against the associated guiderail such that any vibrations caused by imperfections in the guiderails or lower offset loads are sufficiently dampened by the suspension before reaching the elevator car. While suspension-based assemblies may adequately dampen lower offset loads, these roller guide assemblies do not provide adequate stiffness for higher offset loads. Rather, suspension-based assemblies provide safeties or stops which limit further travel of the suspension and prevent undesirable contact between the roller guide assemblies and the respective guiderails. Due to the complexity and the number of components involved, suspension-based roller guide assemblies tend to be more costly to implement and maintain.
Other types of elevator systems employ roller guide assemblies with rollers having fixed roller axes. Fixed-axis rollers are typically provided with an elastomeric material having a generally tapered or rounded surface which serves to cushion contact between the rollers and the guiderails. In contrast to suspension-based assemblies, the tapered or rounded area of contact as shown in FIG. 1 provides a nonlinear increase in stiffness as the elastomeric material deforms under load and conforms to the flat surfaces of the guiderails, also known as Hertz contact. While a Hertz contact roller may be a less costly solution which also provides nonlinearly increasing stiffness in response to offset loads, a Hertz contact roller still lacks the ability to provide a sufficiently sharp transition in stiffness at desired deflection points. Moreover, there is a very limited range within which the stiffness exhibited by the roller may be adjusted to meet dampening criteria for different system configurations. Furthermore, the stiffness of such fixed-roller guide assemblies are highly dependent upon the material properties of the elastomer. For instance, the stiffness of the elastomeric materials of Hertz contact rollers may vary considerably with changes in ambient temperature.